WO1993002781A1

WO1993002781A1 - Portable water purification system

Info

Publication number: WO1993002781A1
Application number: PCT/AU1992/000406
Authority: WO
Inventors: Michel Serge Maxime Lefebvre
Original assignee: Astroa Pty. Limited
Priority date: 1991-08-02
Filing date: 1992-08-03
Publication date: 1993-02-18

Abstract

A manually-operated membrane ultrafiltration system (1) comprises a low-pressure hollow fibre ultrafiltration membrane cartridge or tube (2) operatively connected to a hand-operated pump (4). The membrane has a reticulated fractal structure which greatly enhances the transmission/flux properties of the membrane, enabling the production of sterile ultrafiltered water without the aid of external utilities such as electric pumps. This provides the basis for a portable emergency water sterilisation system of use in areas where natural disasters have occurred, such as floods or earthquakes, particularly where electricity is no longer available as a power source. In such situations, although untreated or contaminated water is readily available, supplies of purified or sterile water are often non-existent.

Description

PORTABLE WATER PURIFICATION SYSTEM

Technical Field

The present invention relates to a system for manually producing purified or sterile potable water from any available fresh water source, even polluted or contaminated sources. The system comprises a hand-operated ultrafiltration pump designed for one person operation. Background Art

The availability of safe drinking water is a critical health need. Water is the substance which makes Earth a unique planet. However, in the developing world, more than half the rural population still do not have access to safe water. This leads to a major health problem: while water is indispensable to the support of life, it is also a major medium of disease transmission. Diarrhoeal diseases cause 5-10 million deaths per year in Africa, Asia and south- America. Viruses are known to be responsible for most of these diseases. The use of safe water and good hygiene are simple environmental measures that can prevent disease transmission.

The transmission of water-borne diseases is likely to be facilitated by the changes in the environment that floods and other natural hazards produce. Natural disasters frequently disrupt supply systems and cause contamination of water sources. Numerous situations exist where a purified or sterile water supply is required but is either not available or not readily available, even though untreated water is readily available. For example, in areas where natural disasters have occurred, such as floods and earthquakes, where normal, orderly systems of communications and supply have broken down, treated - and especially sterile - sources of water are not readily available, and sickness and disease tends to spread virtually unchecked. The young, the elderly and the sick members of localised populations are especially vulnerable. Floods which have occurred in recent years in Bangladesh and China are typical examples . However, localised flooding which has occurred from time to time in developed countries can and has resulted in similar problems - even if on a smaller scale - when the normal orderly communications and supply systems are disrupted. similar problems exist in countries which have been ravaged by war, where orderly systems of communication and supply have been disrupted, and traditional sources of water supply are either no longer available or are unreliable. Such problems were witnessed during the war situation which existed in Iraq in early 1991, where treated or sterile water supplies were no longer available ^'for such applications as mixing with infant milk formula. Untreated sources of water were used to mix infant formula, sickness and disease spread, and there was an unacceptably high infant mortality rate.

In such situations, although untreated water is readily available, purified or sterile water is often non-existent. From previous experience it is known that, in tropical areas, water-borne diseases can develop in a water supply within 48 hours of the occurrence of a catastrophic event. In more temperate areas, water can become contaminated with water-borne diseases within one week, with the potential for sickness and disease to spread rapidly. Although portable water treatment plants are known according to the prior art, they are often of no use in the type of situations described above because they have pumping means which require either a local supply of electricity, or portable electricity generators, which are not always readily available in such situations.

Previously, the only other available membrane water sterilisation means have been high-pressure ultrafiltration (up to 7-8 atmospheres operating pressure) or reverse osmosis (up to 50 atmospheres operating pressure) systems, which ^' require an independent power supply for their operation. Other systems which have been used include: biofiltration (microfiltration), which does not eliminate all virus; chemical treatment, which does not safely sterilise the water in all cases due to difficulty in determining the amount or dose required for sterilisation; and boiling the water, which is slow and impractical. Disclosure of the Invention

It is an object of the present invention to provide a system for manually producing purified or sterile water from available water sources. It is a requirement of such a system that it be light in weight, low cost, and readily simple to operate.

It is another object of the present invention, according to another aspect of embodiment thereof, to provide a low-pressure hollow fibre membrane tube or unit, suitable for use in a manually-operated water purification system, having treated water dispensing means which prevents back-flow and possible contamination of the treated water.

It is a further object of the present invention, according to a further aspect of embodiment thereof, to provide a low-pressure hollow fibre membrane tube of unit, suitable for use in a manually-operated water purification system, including means to automatically stem the flow of water through broken hollow fibres to prevent the contamination of treated water by untreated water within the membrane tube or unit itself. According to one aspect of the present invention there is provided a portable, manually-operable water treatment system comprising manual pumping means operatively connected to a low-pressure hollow fibre membrane tube unit, means for supplying untreated water to the system, and means for dispensing treated water therefrom.

According to another aspect of the invention, the outlet for dispensing the treated/sterile permeate from the water treatment system is adapted to be open only under positive pressure from within the system, to ensure that only treated water can flow out form the permeate side of the hollow fibre tube unit. At other times, the outlet is closed to the ingress of water or air from the outside. According to a further aspect of the invention, means are provided to automatically stem the flow of liquid through individual hollow fibres when the fibre is broken.

This is to prevent contamination of the treated liquid by tlie untreated liquid.

The above , and other objects of the invention, will be apparent from the following description. Brief Description of the Invention

The invention will be further described with reference to the drawings relating to non-limiting embodiments of the invention, in whic :-

Fig. 1 is a schematic illustration of a portable water purification filter and pump according to one embodiment of the invention. Fig. 2 is a frontal elevational view of another embodiment of the invention wherein the pump and the hollow fibre tube unit are disposed in parallel or side-by-side configuration.

Fig. 3 is a side elevational view of the embodiment of Fig. 2.

Fig. 4 is a schematic cross-section of a hollow fibre membrane tube of a type which can be used in the present invention.

Fig. 5 schematically illustrates a further embodiment of a hollow fibre membrane tube which can be used in the present invention.

Fig. 6 illustrates an. embodiment of the permeate sterile water outlet of the portable water purification filter of the present invention. Best Mode of Carrying out the Invention

Referring to Fig. 1 of the drawings, there is shown a portable emergency water purification system 1 comprising a hollow fibre membrane cartridge or tube 2 operatively connected at one end to th outlet 3 of a manual or hand- operated pump 4 which is operated by means of a handle or lever 5. The water inlet 6 to the pump comprises an elongated tube 7 which extends at its lower end into the water source 8 to be treated.

Ideally, the inlet tube 7 to the pump, includes coarse filtration means to exclude coarser material which would foul the hollow fibre membranes. In one embodiment as shown in Fig. 1 the end of the inlet tube which is to be placed into the untreated water supply has a closed end 9 and fine slits or holes 10 through the sidewalls which open under negative pressure from the pump to allow ingress of water.

Referring to Fig. 1, the untreated water from the outlet 3 of pump 4 enters one end of the hollow fibre membrane tube 2 and into an entry manifold chamber 11 where the water is diverted through multiple tubular hollow fibre membranes 12. The permeate (i.e., treated/sterile water), which passes through the walls of the individual hollow fibres and into the inner space of the jacket 13 surrounding the bundle of hollow fibre membranes, is collected from the treated water outlet 14 into clean sterile containers, such as tubular bags sealed at one end, provided in continuous roll packaging. The filled containers can then be sealed at their inlet end, suitable for storage or transport if they are not intended to be used immediately. The retentate, or water which passes through the centre or lumen of the hollow fibre tubes but not through the walls of the hollow fibres to the permeate side, is the residual of the untreated water which collects in the outlet manifold chamber 15 and can be passed off to drain through the outlet 16.

An alternative embodiment of the portable emergency water purification system is illustrated in Figs. 2 and 3 where similar numbering of components is used to that used in Fig. 1 to indicate similar or like components. In this embodiment the pump 4 and the membrane tube unit 2 are mounted in parallel or side-by-side configuration.

Ideally, the portable system is adapted for attachment to a leg, or other part of the body, of the operator_f whereby the pumping means can be operated with one hand, having the other hand free to collect treated water in a suitable container from the dispensing outlet of the system. For example, with the portable system strapped by Velcro^/ straps to the calf or thigh of the operator, the inlet tube or conduit is placed into an available water source (e.g. low-level flood water in which the operator is standing), the operator operates the pump lever with one hand, and the untreated water is pumped into the feed inlet of the hollow fibre tube unit.

Figure 4 is a schematic cross-section of a hollow fibre ultrafiltration membrane tube which comprises a polycarbonate outer jacket 17 enclosing a bundle 18 of hollow fibres ultrafiltration membranes potted at each end into the jacket using a polyurethane potting compound 19. End 'caps 20 and -21 are attached to the jacket by silicone washers or O-rings 22 and 23, and each are provided with connectors 24 and 25 for attaching feed inlet and outlet tubes, respectively. Conventionally, the wide bore connector 24 serves as the inlet and the narrow bore connector 25 is the outlet.

The jacket 17 is provided with alternate outlets 26 and 27 for permeate (e.g. sterile water) which has passed through the walls of the ultrafiltration membrane fibres into the inner space of the jacket surrounding the fibres. Where only one permeate outlet is required the other outlet (in this case 27) is sealed with a removable cap 28. In practise, an inlet tube of water to be ultrafiltered is attached to inlet connector 24. The excess (reject) water can be channelled from outlet connector 25. The ultrafiltered water is collected from outlet 26 (or from outlet 27) into a suitable container. In the event of clogging or fouling of the face of the bundle of hollow fibre membranes in the entry manifold chamber (11 in Fig 1.), the hollow fibre tube unit can be reversed, or the direction of the water through the tube unit can be reversed (i.e., by interchanging the inlet and the outlet tubes) thereby reversing the direction of flow of water through the tube unit, which effectively flushes the fouling material from the face of the bundle of hollow fibres. In effect, with reference to Fig. 1, on reversal of the water flow, the entry manifold chamber is 15 and the outlet manifold chamber is 11.

According to a further aspect of the invention, an embodiment of which is illustrated schematically in Figure 5, means are provided to automatically stem the flow of liquid through individual hollow fibres when the fibre is broken. This is to prevent contamination of the treated liquid by the untreated liquid. In the embodiment depicted in Figure 5, the flow of treated/untreated streams is the reverse of that which exists in the embodiment of Figures 1 and 4. According to the embodiment of Figure 5, the untreated liquid enters through inlet 29 and circulates through the space within the outer jacket of the tube unit i.e., in the space surrounding the hollow fibres, and ^"exits through outlet 30. The permeate in this case is the stream of treated water which passes through the centre or lumen of the hollow fibres, having permeated through the walls of the hollow fibres from the outside to the inside and exits through outlet 31.

The inner walls of each hollow fibre are treated during manufacture to provide them with a coating of non- polymerised latex, obtained by a pre-treatment of the hollow fibres by passing non-polymerised latex, dissolved in a suitable solvent, therethrough. Air is then passed through the lumen and through the walls of the hollow fibres, to remove traces of solvent therefrom, and to maintain the integrity of the pores. As a result, the inner surface of each hollow fibre is coated or lined with a microporous layer of pellicle of non-polymerised latex, which has natural adhesive properties. Under positive pressure from the untreated liquid circulating in the space surrounding each hollow fibre, the fibres have a tendency to collapse, with the walls of individual hollow fibres collapsing upon themselves unless there is permeate circulating therethrough.

In the case of broken fibres, these will also have a

tendency to collapse under the effects of the positive pressure, and will remain closed as the adhesive properties of he latex lining cause portions of the wall to adhere to one another. Thus there is an inbuilt facility to ensure that untreated liquid does not enter the lumen of broken fibres to contaminate the treated stream of liquid.

According to another aspect of the invention, the outlet for dispensing the treated/sterile permeate from the water treatment system is adapted to be open only under positive pressure from within the system, to ensure that only treated water can flow out form the permeate side of the hollow fibre tube unit. At other times, the outlet is closed to the ingress of water or air from the outside. According to this aspect of the invention the dispensing outlet for the treated/sterile water ideally includes outlet holes or slits which are open only under positive pressure from the pump, and which are otherwise normally closed to prevent contamination of treated water from, or back flow of water (or air) into, the treated water area of the system. One possible arrangement according to the present invention is illustrated in Fig. 6, wherein one or more restrictions, as at 31, are provided along the permeate outlet tube 32 which expand to the open state under the influence of applied positive pressure from within the tube unit when treated water is being dispensed. When the pump is not operative, and the system is at rest, the restriction^) return to the normal unexpanded condition, closing off the outlet. This can be achieved during thermoforming of the outlet of the tube unit by varying the level of sintering.

For the production of sterile water, the hollow fibre tube unit of choice is a low-pressure ultrafiltration membrane unit with thin-walled fibres (e.g. ratio of wall thickness to diameter of about 1:20), having a molecular weight cut off of about 10,000. However, where a lesser degree of purification is required, the hollow fibre tube unit need only be a microfiltration membrane unit, or a biofilter, with pore diameters of a fraction of a micron.

Suitable low-pressure ultrafiltration membranes can be manufactured based on procedures described in, for example, Australian Patent No. 576364 (equivalent to U.S. Patent No. 4749487) operating at low inlet pressure (e.g. about 50-70 kPa) with a permeate flow rate of about one litre of sterile (bacteria and virus-free) pyrogen-free water per minute. Such a unit is capable of manually producing enough sterile drinking water to satisfy the needs of 400-1000 people for up to three months before the membrane tube would require replacement.

The above-mentioned patent relates to the surface treatment of commercially available hollow fibre membranes to create so-called "fractal" membranes or membranes having a surface of fractal geometry, being highly convoluted or reticulated.

To develop a fractal membrane a semipermeable membrane is required which comprises: a macroporouε substrate such as a conventional biofilter, a microporous microskin having a surface of fractal geometry permanently deposited on the substrate.

Since the substrate only constitutes a support, the material of which it is formed will only be chosen bearing in mind the conditions of formation of the microskin and of operation of the membrane. If a resistance to high temperature is required, stainless steel or a ceramic material will be used; ceramic material for high solvent resistance; and certainly an inert polymeric material, such as polypropylene, for high acid/alkali resistance. For water treatment, a supporting substrate of polypropylene is used onto which is placed a heat, acid and alkali resistant, negatively charged microskin which is densely convoluted or reticulated. Ideally, a polypropylene/ceramic composite membrane is used.

A method of producing the microskin is to deposit on the substrate a liquid-containing gel layer, to remove liquid from the gel layer which is then treated to become permanently fixed on the support and shrunk to develop a pleated reticulated fractal surface.

In practise, a microskin of reticulated surface may be achieved by using a gel formed from a tribasic compound such as calcium aconitate, aluminium hydroxide or phosphoric acid. It may also be possible to use a divalent compound which is reacted with other materials. The reticulated structure is generated by the molecular rearrangement caused by removal of liquid from the gel.

Being a surface treatment of membranes, this treatment applies to any existing membranes. In fact the treatment is generally conducted "in situ".

The treatment is conducted in three steps: - Creation of a dynamic membrane on to the surface of porous support by filtration of a colloid material obtained by polymerisation of monomers having three different functions (for example two acid, one base) or copolymerisation between monomers for the end polymer to establish these three functions (for example anionic and cationic surfactants) . - Thickness reduction of this layer.

Compaction and reticulation which involves elimination of part of the solvent (for example solvent expulsion .by pH change).

The reticulated fractal structure has a great impact on the transmission properties of the membrane. Fractal surfaces have very high surface area per unit topological area and, if charged, have unusual apparent surface densities giving exceptional repulsion characteristics. The preferred negatively charged fractal ultrafiltration membrane used for water sterilisation has a charge density of no less than 600 coulombs/cm³, with high resistance to membrane fouling. The following are the specifications of a preferred fractal ultrafiltration membrane cartridge or tube used in the portable emergency water purification pump according to the present invention: Cartridge size: 0.4m² (area in square metres) Dimensions: Length 220mm; diameter 50mm Weight: 300gm Materials: Outer jacket - polycarbonate

Hollow fibres - polypropylene and ceramic composite, 200 micron internal diameter

Pore size: 100 Angstrom (0.01 microns)

Molecular Weight 20,000 daltons cut-off: at 50% rejection

Max. operating pressure: 120 kPa (1.2 bar; 18 psi)

Max operating temp: 60°

Water flux: 130 litres/m²/hour at 100 kPa (1 Atmosphere) pH range: 0-14 Charge density: Greater than 600 coulombs/cm³

When the above preferred fractal ultrafiltration

- membrane cartridge is used in the portable emergency water purification pump according to the present invention, the total weight is less than 1.5 kilograms. The operating pressure of the hand pump is 0.5 - 0.7 Atmospheres (50- 70kPa; 7.5-10.5 psi). The energy requirement for operation is of the order of 15 W/m² (30 W/m² is the approximate limit for manual operation) . Competitive membrane systems operate at 100-700 Watts/m²' and require an electric pump for operation. Used for the sterilisation of water, the fractal ultrafiltration membrane cartridge has a flux at least five times greater than conventional ultrafiltration membranes, with a driving force energy requirement far lower than that for conventional membranes.

The manual pump component of the system may either be purpose-built, or alternatively may comprise a lightweight commercially-available pump. For example, a lightweight hand-operated bilge pump, readily available for marine applications, weighing 0.5-1 kilogram. Ideally, the overall weight of the water treatment system is less than about 1.5 kilograms.

The water produced is sterile and pyrogen-free and as such, whilst it can be used as drinking water, it is of a quality suitable for intravenous and other medical/pharmaceutical applications. As such, the system of the present invention is highly suitable as a portable emergency water sterilisation system for use in emergency or field hospitals. The reliability of the system can be demonstrated with water containing the polysaccharide, blue dextran, the ^■ molecules of which are of dimensions smaller than the smallest virus. The treated water is colourless, which indicates that the blue dextran is not able to pass through the fractal membrane.

The capability to manually produce purified water from contaminated sources, ds provided by the present invention, is also of potential interest as a package for operational military units, especially for use by e.g. civil protection units engaged in relief efforts, or for units equipped with •"ABC protection (i.e. Atomic, Biological and Chemical), where water contamination impairs the operational capability of such units.

The manually-operable water treatment system of the present invention also has potential for use in other applications where an untreated water supply is available and purification is desirable. For example, on construction or mining sites in. remote locations in tropical of sub¬ tropical areas, non-sedentary workers need to regularly replenish salts and electrolytes lost through perspiration, otherwise they become inefficient or - in severe cases - suffer from severe heat exhaustion, which can result in death. It is envisaged that water treatment system of the present invention would provide a convenient means to obtain purified water for mixing with essential salts, prepackaged in the required dosage, in a suitable container ready for use. Although the invention has been described above with reference to drawings and to preferred embodiments, it will be appreciated that the invention may be embodied in other forms or carried out in other ways without departing from the spirit of essential characteristics thereof. The above description is therefore to be considered as in all respects, illustrative and not restrictive, and all changes which come within the meaning and range of equivalency are intended to be embraced herein.

SUBSTITUTESHEET

Claims

CLAIMS : -

1. Apparatus (1) for the membrane purification of a liquid comprising manual pumping means (4) operatively connected to a low-pressure hollow fibre membrane tube unit (2), means (7) for supply untreated liquid (8) to the apparatus, and means (14) for dispensing treated liquid therefrom.

2. Apparatus according to Claim 1, wherein said hollow fibre membrane tube unit 2 comprises a plurality of ultrafiltration microporous hollow fibre membranes (12) and means (14) for dispensing ultrafiltered liquid therefrom.

3. Apparatus according to Claim 1 or Claim 2, wlierein said hollow fibre membrane tube unit (2) comprises a plurality of ultrafiltration hollow fibre membranes (12) each comprising a macroporous substrate having a microporous microskin deposited thereon, the microskin having a surface of fractal geometry.

4. Apparatus according to any one of the proceeding claims, wherein said hollow fibre membranes have a pore size of about 50 to 100 Angstrom and a charge density greater than about 600 coulombs/cm³.

5. Apparatus according to Claim 3 or Claim 4, wherein said hollow fibre membranes comprise a polypropylene substrate having a microporous ceramic microskin deposited thereon having a surface of fractal geometry.

6. Apparatus according to any one of the preceding claims, adapted to operate at a pressure of no more than about 120kPa and an input energy requirement of no more than about 15-20 Watts/m²-

7. Apparatus according to Claim 1, wherein the means for dispensing treated liquid comprises an outlet (32) which is adapted to be only under positive pressure from within the apparatus generated by the pumping means during operation of the apparatus, to ensure that only treated liquid can flow from the hollow fibre membrane tube unit, and wherein when the apparatus is not in operation the outlet is closed (31) to the ingress of air or liquid from the outside of the outlet .

8. Apparatus (1) for the membrane purification of a liquid comprising manual pumping means (4) operatively connected to a low-pressure hollow fibre membrane tube (2) which comprises a tubular housing (2,17); a bundle of microporous hollow fibres (12, 18) arranged within the housing in the axial direction thereof; a treated liquid collection chamber (13) formed between the outer surfaces of the hollow fibre bundle and the inner surface of the housing; an outlet for dispensing treated liquid (14, 26) from said treated liquid collection chamber; partition walls (19) supporting the hollow fibre bundle, separating the open ends of the hollow fibres (11,15) from the liquid collection chamber (13) and defining the length of the said chamber; and inlet (24) and outlet (25) ports for the untreated liquid, said inlet and outlet ports communicating with the interior space of lumen of each of the hollow fibres, and wherein a plurality of pores or channels of predetermined molecular dimensions and permeability communicate between the interior space or lumen of each hollow fibre and the surrounding liquid collection chamber through the walls of each hollow fibre whereby treated liquid may be transferred from the untreated liquid side to the treated liquid side of the membranes to be collected in said collection chamber (13) and dispensed from said outlet (16, 27) for the treated liquid.

9. Apparatus (1) for the membrane purification of a liquid comprising manual pumping means (4) operatively connected to a low-pressure hollow fibre membrane tube unit which comprises a tubular housing; a bundle of microporous hollow fibres arranged within the housing in the axial direction thereof; an untreated liquid chamber formed between the outer surfaces of the hollow fibre bundle and the inner surface of the housing; first inlet (29) and outlet (30) ports for passing the untreated liquid into and out of the said liquid chamber; partition walls supporting the hollow fibre bundle and separating the ends of the hollow fibres from the untreated liquid chamber and defining the length of the said chamber; a second outlet port (31) for the treated liquid at one end of the hollow fibre bundle and communication through one of^' the partition walls with the interior space or lumen of each of the hollow fibres, the other end of the hollow fibres being closed, and wherein a plurality of pores or channels of predetermined molecular dimensions and permeability communicate between the interior space or lumen of each hollow fibre and the surrounding untreated liquid chamber through the walls of each hollow fibre whereby treated liquid may be transferred from the untreated liquid side to the treated liquid side of the membranes being the interior space or lumen of each hollow fibre and dispensed from said second outlet (31).

10. Apparatus according to Claim 9, wherein the inner walls of each hollow fibre membrane are coated with a microporous layer or pellicle of a compound having adhesive properties and are adapted to collapse under positive pressure from the space surrounding the hollow fibre membranes.